Vacuum IG units are known in the art. For example, see U.S. Pat. Nos. 5,664,395, 5,657,607, and 5,902,652, the disclosures of which are all hereby incorporated herein by reference.
FIGS. 1-2 illustrate a conventional vacuum IG unit (vacuum IG unit or VIG unit). Vacuum IG unit 1 includes two spaced apart glass substrates 2 and 3, which enclose an evacuated or low pressure space 6 therebetween. Glass sheets/substrates 2 and 3 are interconnected by peripheral or edge seal of fused solder glass 4 and an array of support pillars or spacers 5.
Pump out tube 8 is hermetically sealed by solder glass 9 to an aperture or hole 10 which passes from an interior surface of glass sheet 2 to the bottom of recess 11 in the exterior face of sheet 2. A vacuum is attached to pump out tube 8 so that the interior cavity between substrates 2 and 3 can be evacuated to create a low pressure area or space 6. After evacuation, tube 8 is melted to seal the vacuum. Recess 11 retains sealed tube 8. Optionally, a chemical getter 12 may be included within recess 13.
Conventional vacuum IG units, with their fused solder glass peripheral seals 4, have been manufactured as follows. Glass frit in a solution (ultimately to form solder glass edge seal 4) is initially deposited around the periphery of substrate 2. The other substrate 3 is brought down over top of substrate 2 so as to sandwich spacers 5 and the glass frit/solution therebetween. The entire assembly including sheets 2, 3, the spacers, and the seal material is then heated to a temperature of approximately 500° C., at which point the glass frit melts, wets the surfaces of the glass sheets 2, 3, and ultimately forms hermetic peripheral or edge seal 4. This approximately 500° C. temperature is maintained for from about one to eight hours. After formation of the peripheral/edge seal 4 and the seal around tube 8, the assembly is cooled to room temperature. It is noted that column 2 of U.S. Pat. No. 5,664,395 states that a conventional vacuum IG processing temperature is approximately 500° C. for one hour. Inventor Collins of the '395 patent states in “Thermal Outgassing of Vacuum Glazing,” by Lenzen, Turner and Collins, that “the edge seal process is currently quite slow: typically the temperature of the sample is increased at 200° C. per hour, and held for one hour at a constant value ranging from 430° C. and 530° C. depending on the solder glass composition.” After formation of edge seal 4, a vacuum is drawn via the tube to form low pressure space 6.
Unfortunately, the aforesaid high temperatures and long heating times of the entire assembly utilized in the formulation of edge seal 4 are undesirable, especially when it is desired to use a heat strengthened or tempered glass substrate(s) 2, 3 in the vacuum IG unit. As shown in FIGS. 3-4, tempered glass loses temper strength upon exposure to high temperatures as a function of heating time. Moreover, such high processing temperatures may adversely affect certain low-E coating(s) that may be applied to one or both of the glass substrates in certain instances.
FIG. 3 is a graph illustrating how fully thermally tempered plate glass loses original temper upon exposure to different temperatures for different periods of time, where the original center tension stress is 3,200 MU per inch. The x-axis in FIG. 3 is exponentially representative of time in hours (from 1 to 1,000 hours), while the y-axis is indicative of the percentage of original temper strength remaining after heat exposure. FIG. 4 is a graph similar to FIG. 3, except that the x-axis in FIG. 4 extends from zero to one hour exponentially.
Seven different curves are illustrated in FIG. 3, each indicative of a different temperature exposure in degrees Fahrenheit (° F.). The different curves/lines are 400° F. (across the top of the FIG. 3 graph), 500° F., 600° F., 700° F., 800° F., 900° F., and 950° F. (the bottom curve of the FIG. 3 graph). A temperature of 900° F. is equivalent to approximately 482° C., which is within the range utilized for forming the aforesaid conventional solder glass peripheral seal 4 in FIGS. 1-2. Thus, attention is drawn to the 900° F. curve in FIG. 3, labeled by reference number 18. As shown, only 20% of the original temper strength remains after one hour at this temperature (900° F. or 482° C.). Such a significant loss (i.e., 80% loss) of temper strength is of course undesirable.
In FIGS. 3-4, it is noted that much better temper strength remains in a thermally tempered sheet when it is heated to a temperature of 800° F. (about 428° C.) for one hour as opposed to 900° F. for one hour. Such a glass sheet retains about 70% of its original temper strength after one hour at 800° F., which is significantly better than the less than 20% when at 900° F. for the same period of time.
Another advantage associated with not heating up the entire unit for too long is that lower temperature pillar materials may then be used. This may or may not be desirable in some instances.
Even when non-tempered glass substrates are used, the high temperatures applied to the entire VIG assembly may melt the glass or introduce stresses. These stresses may increase the likelihood of deformation of the glass and/or breakage.
Thus, it will be appreciated that there is a need in the art for a vacuum IG unit, and corresponding method of making the same, where a structurally sound hermetic edge seal may be provided between opposing glass sheets. There also exists a need in the art for a vacuum IG unit including tempered glass sheets, wherein the peripheral seal is formed such that the glass sheets retain more of their original temper strength than with a conventional vacuum IG manufacturing technique where the entire unit is heated in order to form a solder glass edge seal.
An aspect of certain example embodiments of this invention relates to applying localized heating to the periphery of a unit to form edge seals to reduce the heating of the non-peripheral areas of the unit and thereby reduce the chances of the substrates breaking.
An aspect of certain example embodiments relates to providing staged heating, localized heating, and staged cooling of a unit via a unitized oven, the localized heating being provided by a substantially linear focused infrared (IR) heat source comprising an array or matrix of linear heat sources.
Another aspect of certain example embodiments relates to providing a vacuum IG unit having a peripheral or edge seal formed so that at least certain portion(s) of thermally tempered glass substrates/sheets of the vacuum IG unit retain more of their original temper strength than if conventional, edge seal forming techniques were used with the solder glass edge seal material.
Another aspect of certain example embodiments relates to providing a vacuum IG unit, and method of making the same, wherein at least a portion of the resulting thermally tempered glass substrate(s) retain(s) at least about 50% of original temper strength after formation of the edge seal (e.g., solder glass edge seal).
Another aspect of certain example embodiments relates to reducing the amount of post-tempering heating time necessary to form a peripheral/edge seal in a vacuum IG unit.
In certain example embodiments of this invention, there is provided a method of making a vacuum insulating glass (VIG) window unit, the method comprising: providing first and second substantially parallel spaced-apart glass substrates and a frit provided at least partially between the first and second glass substrates for sealing an edge of the VIG window unit; pre-heating the glass substrates and the frit to at least one temperature below a melting point of the first and second substrates and below a melting point of the frit; providing localized near infrared (IR) inclusive heat via at least one substantially two-dimensional array of heat sources proximate to the edge to be sealed so as to at least partially melt the frit; and cooling the unit and allowing the frit to harden in making the vacuum insulating glass (VIG) window unit.
In certain example embodiments of this invention, a method of making a vacuum insulating glass unit including an edge seal thereof is provided. There is provided a unit comprising first and second substantially parallel spaced-apart glass substrates, one or more edges between the first and second substrates to be sealed, and a frit for sealing each said edge to be sealed. The unit is pre-heated in its entirety to at least one intermediate temperature, each said intermediate temperature being below a melting point of the first and second substrates and below a melting point of the frit. Via near infrared radiation generated via at least one substantially two-dimensional array of heat sources, localized heat is provided to the unit proximate to the edges to be sealed at a frit melting temperature, the frit melting temperature being sufficiently high to melt the frit, the localized heat being provided to the unit such that areas of the unit not proximate to the edges to be sealed are maintained at a temperature close to an intermediate temperature. The unit is cooled in its entirety to at least one reduced temperature and the fit is allowed to harden.
In certain example embodiments, a method of making an edge seal for a vacuum insulating glass unit is provided. An oven including entrance, edge sealing, and exit zones is provided. A unit comprising first and second substantially parallel spaced-apart glass substrates, one or more edges between the first and second substrates to be sealed, and a frit for sealing each said edge to be sealed is inserted into the oven. In the entrance zone of the oven, the unit is pre-heated in its entirety to at least one intermediate temperature, each said intermediate temperature being below a melting point of the first and second substrates and below a melting point of the frit. In the edge sealing zone of the oven, there is provided, via a localized heat source comprising at least one substantially two-dimensional array of heat sources, localized heat to the unit proximate to the edges to be sealed at a frit melting temperature, the frit melting temperature being sufficiently high enough to melt the frit, the localized heat being provided to the unit such that areas of the unit not proximate to the edges to be sealed are maintained at a temperature close to an intermediate temperature. In the exit zone of the oven, the unit is cooled in its entirety to at least one reduced temperature and the frit is allowed to harden.
In certain example embodiments, an apparatus for forming edge seals for vacuum insulating glass units is provided. An entrance zone is provided for receiving a unit comprising first and second substantially parallel spaced-apart glass substrates, one or more edges between the first and second substrates to be sealed, and a frit for sealing each said edge to be sealed, and for pre-heating the unit in its entirety to at least one intermediate temperature, each said intermediate temperature being below a melting point of the first and second substrates and below a melting point of the frit. An edge sealing zone including, a localized heat source comprising at least one substantially two-dimensional array of heat sources is provided for providing localized heat to the unit proximate to the edges to be sealed at a frit melting temperature, the frit melting temperature being sufficiently high enough to melt the frit, the localized heat being provided to the unit such that areas of the unit not proximate to the edges to be sealed are maintained at a temperature close to an intermediate temperature. An exit zone of the oven is provided for cooling the unit in its entirety to at least one reduced temperature and allowing the frit to harden.
In certain example implementations, the heat sources in the array are arranged in a plurality of rows and columns, and the rows and/or columns are staggered in certain example implementations. In certain example implementations, each heat source in each row and column of the array may be selectively activated in dependence on whether an edge to be sealed is proximate to the heat source.
The features, aspects, advantages, and example embodiments described herein may be combined to realize yet further embodiments.